JP4534031B2 - Organic EL display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to black level setting in an organic EL device.
[0002]
[Prior art]
FIG. 1 shows a configuration example of a circuit (pixel circuit) for one pixel in an active organic EL display device. The drain of the P-channel driving TFT 1 whose source is connected to the power supply line PVdd is connected to the anode of the organic EL element 3, and the cathode of the organic EL element 3 is connected to the cathode power supply CV. The gate of the driving TFT 1 is connected to the source of the N-channel selection TFT 2, the drain of the selection TFT 2 is connected to the data line Data, and the gate is connected to the gate line Gate. In addition, one end of the storage capacitor C is connected to the gate of the driving TFT 1 and the other end is connected to the capacitor power supply line Vsc.
[0003]
Therefore, the gate line extending in the horizontal direction is set to the H level, the selection TFT 2 is turned on, and the data signal having a voltage corresponding to the display luminance is put on the data line Data extending in the vertical direction in this state. Accumulated in the storage capacitor C. As a result, the driving TFT 1 supplies a driving current corresponding to the data signal to the organic EL element 3, and the organic EL element 3 emits light.
[0004]
Here, the light emission amount of the organic EL element and the current are in a substantially proportional relationship. Usually, a voltage (Vth) is applied between the gate of the driving TFT 1 and PVdd so that the drain current starts to flow near the black level of the image. In addition, as the amplitude of the image signal, an amplitude that gives a predetermined luminance near the white level is given.
[0005]
FIG. 2 shows the relationship of the current icv (corresponding to the luminance) flowing in the organic EL element 3 with respect to the gate-source voltage Vgs (difference between the data line Data voltage and the power source PVdd) of the driving TFT 1. By determining the data signal so that Vth is applied as the black level voltage and Vw is applied as the white level voltage, appropriate gradation control in the organic EL element 3 can be performed.
[0006]
However, the Vth varies with temperature, external light, and the like. That is, due to changes in the usage environment of the panel, self-heating, etc., the luminance of the image changes, and phenomena such as blackening and blacking occur.
[0007]
As a result, an excessive current flows through the panel, which may accelerate the deterioration of the OLED element. In order to limit the current flowing through the display panel, a method has been proposed in which the total current of the panel is detected to change the contrast and luminance level of the input signal (Patent Document 1).
[0008]
[Patent Document 1]
JP 2002-251167 A
[0009]
[Problems to be solved by the invention]
However, the method described in Patent Document 1 only limits the current flowing through the display panel, cannot correct the change in the black level or the white level with respect to the environmental change, and is appropriate when the environment changes. The display could not be maintained.
[0010]
The present invention relates to displaying a stable image by appropriately adjusting luminance and black level even when the characteristics of an organic EL display element change due to environmental changes or self-heating.
[0011]
[Means for Solving the Problems]
The present invention is an organic EL display device having a display panel formed by arranging a plurality of organic EL elements, each of which includes an organic EL element and a plurality of pixels each including a driving thin film transistor having a drain connected to the organic EL element. The display data for each pixel related to the display image to be displayed on the display panel is shifted according to the black level voltage setting value, and is supplied to the display panel, and black level setting means for creating a drive command for each organic EL element Display data calculation means for calculating an estimated current value corresponding to the current flowing in the display panel based on display data, panel current detection means for detecting panel current flowing in all pixels of the display panel, and the display data calculation means Comparing the estimated current value obtained with the panel current for the corresponding display detected by the panel current detection means Comparison means that, according to the comparison result of the comparing means, have a, and adjusting means for adjusting the black level voltage setting value, the display data stored in the storage capacitor connected to the gate of the driving TFT The magnitude of the drive current is controlled .
[0012]
Thus, according to the present invention, the panel current estimated from the display data is compared with the actual panel current, and the black level voltage setting value is adjusted according to the comparison result. Even when the characteristics of the organic EL element change, this can be compensated to maintain an appropriate display.
[0013]
The display data calculation means calculates an estimated current value from the current flowing through the display panel when an ideal display based on the sum or average value of the display data is performed, and the adjustment means is calculated by the comparison means. It is preferable to adjust the black level based on the difference.
[0014]
Moreover, it is preferable to further have an environment estimation means for estimating the environment where the organic EL display panel is placed according to the comparison result of the comparison means. Examples of the environment to be estimated include temperature and presence / absence of incident light. By estimating these environments, it is possible to cope with the environment. For example, it is possible to start the cooling means for the temperature rise, decrease the display luminance, and increase the luminance for the presence of incident light.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0016]
FIG. 3 shows the configuration of the embodiment. A video signal composed of image data for each pixel is input to the gamma correction circuit 10, and is corrected so that the current flowing through the image data and the pixel has a linear relationship by a preset gamma characteristic. The video signal subjected to gamma correction for each image data is supplied to the adder 12, where the black level setting value is added. Thereby, the output of the adder 12 becomes data relating to the drive current for each pixel. The output of the adder 12 is supplied to the D / A converter 14 where it is converted into an analog signal, which is supplied to the organic EL panel 16.
[0017]
The organic EL panel 16 is configured by arranging pixel circuits as shown in FIG. 1 in a matrix. The signal from the D / A converter 14 is temporarily stored in the peripheral drive circuit of the organic EL panel 16, and the drive TFT of each pixel is driven based on the stored signal for each pixel, and the corresponding organic The EL element emits light.
[0018]
A power source PVdd is connected to the organic EL panel 16, and a driving current of all organic EL elements is supplied from the power source PVdd and a current detector 18 is connected to detect the total current flowing through the organic EL panel 16. To do. That is, the current from the power source PVdd flows in each organic EL element of the organic EL panel 16 according to the display data, and the sum (panel current) is detected by the current detector 18. Each pixel circuit of the organic EL panel 16 has a storage capacitor and emits light for a period of approximately one frame. Therefore, the current detector 18 can detect the entire current of one frame. In addition, since the organic EL panel 16 writes data in a dot-sequential manner, it is also preferable to detect the total current in the vertical blanking period after all the image data is written. Further, the integrated current in several frames may be detected instead of the total panel current in one frame, and the average current may be calculated from the integrated current. Further, an average current for a predetermined period in one frame or an integrated current may be used.
[0019]
The detection result of the current detector 18 is converted into digital data by the A / D converter 20 and then supplied to the adder 22. The adder 22 is supplied with estimated current data of the input video signal from the current calculator 24 as negative data. This estimated current data corresponds to a panel current flowing in the organic EL panel 16. Therefore, the adder 22 compares the data (panel total current) about the current value corresponding to the light emission luminance in the organic EL panel 16 detected by the current detector 18 with the estimated current data of the input video signal, and the difference between them. Is calculated.
[0020]
Here, what is detected by the current detector 18 is a current value obtained by performing gamma correction on the input luminance data of each pixel, adjusting the black level, and inputting it to the panel. For this reason, it corresponds to the estimated current data for one frame of the video signal.
[0021]
Therefore, the current calculation unit 24 performs the following conversion. That is, Y = (average of image data for one frame) × A, and this Y is input to the adder 22. Here, the coefficient A is, for example, A = Iy ₀ / y ₀ . Iy ₀ is adjusted to the optimum black level and optimum maximum luminance under the normal use environment, and the total current of the pixel part (panel total current) when the image of the average level y0 (the luminance data is all y ₀ for all pixels) is displayed. The total panel current after gamma correction and black level adjustment. As a result, the output from the current calculation unit 24 corresponds to the total panel current when the image data of the video signal for one frame is displayed on the organic EL panel 16 and subjected to gamma correction and black level adjustment. It will be. When the current detected by the current detector 18 is not one panel total panel current, the value calculated by the current calculation unit 24 also corresponds to the value detected by the current detector 18.
[0022]
Therefore, as the output of the adder 22, the difference between the total current of the organic EL panel 16 that should be based on the luminance of one frame of the video signal and the panel total current of the organic EL panel 16 that is actually detected is calculated. Become.
[0023]
The difference calculated in the adder 22 is supplied to the LPF 26, where it is smoothed to remove large fluctuations and to prevent instability due to an abrupt response. The output of the LPF 26 is multiplied by the loop gain K in the K multiplier 28 and then supplied to the adder 30. Here, the loop gain K determines the strength of the correction, and the larger the loop gain K is, the closer it can be to the set value (initial adjustment value).
[0024]
A black level set value is supplied to the adder 30, and this black level set value is added to the output of the K multiplier 28. Here, the black level setting value is usually data on the optimum black level under the normal use environment described above, and is a value indicated by Vth in FIG.
[0025]
In this way, the optimum black level data is corrected by the data from the adder 22 and supplied to the adder 12. Therefore, when the characteristics change to the characteristics such as a and b shown by the broken lines in FIG. 2 according to the change in the operation state and environment, the characteristics are shifted correspondingly and the black level is automatically adjusted. Become. That is, when Vth changes due to temperature, external light, etc., the total panel current in the current detector 18 changes accordingly. Accordingly, the change in the adder 22 is taken out as a difference, and the result obtained by multiplying the change by the predetermined gain K is added to the display data in the adder 12 via the adder 30, so that the change is caused by the change in Vth. It is possible to effectively prevent the occurrence of a phenomenon such as a change in brightness of the image, blackening, and blackening.
[0026]
"Other embodiments"
In the above-described embodiment, a monochrome panel has been described as an example. However, if the current of each color can be individually detected by the color panel, the above-described control may be performed for each color. On the other hand, in a color panel, the current of each color cannot be measured individually from the outside in many cases. In this case, as shown in FIG. 4, R signal, G signal, and B signal are received separately. And it has gamma correction circuits 10R, 10G, 10B, adders 12R, 12G, 12B, and D / A converters 14R, 14G, 14B.
[0027]
The R signal, the G signal, and the B signal are respectively input to the three gamma correction circuits 10R, 10G, and 10B, and the gamma correction circuits 10R, 10G, and 10B respectively perform gamma correction. The outputs of the gamma correction circuits 10R, 10G, and 10B are added to the adjusted black level correction values from the adder 30 in the adders 12R, 12G, and 12B, and then added to the D / A converters 14R, 14G, and 14B. It is converted into an analog signal and supplied to the organic EL panel 16. The organic EL panel 16 has separate display pixels for RGB, and the light emission of these pixels is controlled by RGB separate luminance signals to perform color display.
[0028]
Here, in this apparatus, in the current calculation unit 24,
Y = R * Ar + G * Ag + B * Ab
Perform the operation.
[0029]
Here, R, G, and B are luminance data of the input R signal, G signal, and B signal, Ar = Ir ₀ / r ₀ , Ag = Ig ₀ / g ₀ , Ab = Ib ₀ / b ₀ It is.
[0030]
Also,
Ir _0: Normal use was adjusted to the optimum black level and the optimum maximum brightness in the environment, the average level r red pixels of the panel total current r ₀ when the red single-color image displaying the _0: used to measure Ir ₀ The average level Ig ₀ of one frame of red single-color still image data: The panel total current g of green pixels when a green single-color image of average level g ₀ is displayed by adjusting to the optimum black level and optimum maximum luminance under normal use environment ₀ : Average level of one frame of green single-color still image data used for measuring Ig ₀ Ib ₀ : Adjusted to the optimum black level and optimum maximum luminance in a normal use environment, and a blue monochrome image of average level b ₀ This is the average level of one frame of blue single-color still image data used to measure the total panel current b ₀ : Ib ₀ of the blue pixel when displayed.
[0031]
Accordingly, the total current for displaying each color to be determined in accordance with the luminance level of each RGB signal is calculated, and this is compared with the total panel current actually flowing through the panel, and the difference is output from the adder 22. It will be.
[0032]
In this way, by comparing the average panel total current based on the input RGB signals and the actual panel total current, the variation can be compensated for and appropriate display can always be performed.
[0033]
Further, as shown in the figure, it is also preferable to supply a smoothed difference signal, which is the output of the LPF 26, to the CPU. As a result, the value of the output of the LPF 26 or the adder 22 when a specific image is displayed can be read by the CPU to know the change in the environment. For example, when the characteristics of the panel are not affected by changes other than temperature changes, or when environmental changes other than temperature changes are known and changes in characteristics are known, temperature changes can be read from this value. Similarly, if the temperature change and other environmental changes other than the light incident on the panel are known, the light incident on the panel can be known. Therefore, in response to such changes in the environment, a process that suppresses heat generation (for example, reduction of luminance, stop of display), cooling (for example, driving of a fan or a cooling element), or incident light A display corresponding to a certain thing (for example, an increase in luminance) can be performed. Furthermore, it is possible to prompt the user to deal with the situation by displaying the countermeasure when the temperature rises or incident light is present.
[0034]
FIG. 5 shows examples of characteristics that can be used instead of the K multiplier. As in (a), K = 0 is not corrected within a certain range where Vth varies, and only when the range is exceeded, K is set as a predetermined value and a correction amount proportional to the difference is output. You can also. Further, as shown in (b), when the input is negative when the input is negative, it is possible to correct only the blackening, and conversely, when the input is positive when the input is positive, only the black crushing is corrected. be able to.
[0035]
Moreover, it can also be set as the structure shown in FIG. In this configuration, the output of the A / D converter 20 is supplied to the CPU 40, and the output of the current calculation unit 24 is also supplied to the CPU 40. Then, the CPU 40 supplies the adjusted black level setting value to the adder 12. In such a configuration, the total panel current supplied from the A / D converter 20 is read by the CPU 40 periodically (for example, every few seconds), and the current that should flow and the actual current for the currently displayed image. And the black level set value is changed by estimating the change in Vth. That is, the CPU 40 performs all the operations of the adder 22, LPF 26, K multiplier 28, and adder 30 in FIG. Furthermore, the operation of the current calculation unit 24 can also be performed by the CPU 40.
[0036]
In this example as well, full-color (RGB) display can be handled in the same manner as in FIG.
[0037]
Furthermore, similar control may be performed by providing dummy pixels in a part of the panel and monitoring the characteristics of the pixels during panel operation. That is, the dummy pixel is provided in a region where light is not emitted by covering a region where the display cannot be seen or the front surface, and arbitrary display data is supplied to the dummy pixel, and a current flowing through the pixel is detected. Then, by comparing the estimated current of the dummy pixel and the current that actually flows, a change in the environment in which the panel is placed can be reliably detected.
[0038]
As described above, according to the present embodiment, the black level voltage adjustment of the panel input is performed by calculating the difference between the sum or average of data of one frame or several frames of the image driving the panel and the total panel current flowing in all the pixels of the panel. Returning to the value, the optimum black level input voltage is always supplied to the panel even when Vth changes.
[0039]
In the active matrix organic EL panel, data of each pixel is normally held for one frame period by a capacitor added to the gate of the pixel driving TFT. Therefore, when the current flowing through the pixel is proportional to the image data, the panel total current of the pixel portion of the OLED panel at a certain point is proportional to the sum of the image data input one frame before that point. It is in. By measuring this proportionality constant in advance, the total current of the pixel portion in units of frames can be estimated from the image data. When the panel total current is larger than this estimated value, it is considered that Vth is shifted in the direction of a in FIG. 2, and the black level of the signal input to the panel is also shifted in that direction. Conversely, when the total panel current is small, it is considered that Vth is shifted in the direction of b in FIG. 2, and the black level of the signal input to the panel is also shifted accordingly. As a result, it is possible to effectively prevent changes in the brightness of the image due to changes in Vth, blackouts, floating blacks, etc., and the characteristics of the organic EL display element change due to environmental changes or self-heating. In addition, the luminance and black level do not change, and a stable image can be displayed.
[0040]
【The invention's effect】
As described above, according to the present invention, the panel current estimated from the display data is compared with the actual panel current, and the black level voltage setting value is adjusted according to the comparison result. Even when the characteristics of the organic EL element change, this can be compensated to maintain an appropriate display.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of a pixel circuit.
FIG. 2 is a characteristic diagram showing a relationship between an input voltage to a driving TFT and light emission luminance.
FIG. 3 is a diagram illustrating a configuration of an embodiment.
FIG. 4 is a diagram showing a configuration of another embodiment.
FIG. 5 is a characteristic diagram illustrating an example of a loop gain.
FIG. 6 is a diagram showing a configuration of still another embodiment.
[Explanation of symbols]
10, 10R, 10G, 10B Gamma correction circuit, 12, 12R, 12G, 12B adder, 14, 14R, 14G, 14B D / A converter, 16 organic EL panel, 18 current detector, 20 A / D converter , 22, 30 adder, 24 current calculator, 28 multiplier, 30 adder, 40 CPU.

Claims (3)

An organic EL display device having a display panel formed by arranging a plurality of organic EL elements,
A plurality of pixels each including an organic EL element and a driving thin film transistor having a drain connected to the organic EL element;
Black level setting means that shifts the display data for each pixel related to the display image displayed on the display panel according to the black level voltage setting value and creates a drive command for each organic EL element;
Display data calculation means for calculating an estimated current value corresponding to a current flowing through the display panel based on display data supplied to the display panel;
Panel current detection means for detecting a panel current flowing in all pixels of the display panel;
Comparison means for comparing the estimated current value obtained by the display data calculation means with the panel current for the corresponding display detected by the panel current detection means,
Adjusting means for adjusting the black level voltage set value according to the comparison result of the comparing means;
I have a,
The organic EL display device, wherein the magnitude of the drive current is controlled by display data stored in a storage capacitor connected to the gate of the drive thin film transistor . The organic EL display device according to claim 1,
The display data calculation means calculates an estimated current value from a current flowing through the display panel when an ideal display based on a sum or average value of display data is performed,
The organic EL display device that adjusts the black level based on the difference calculated by the comparison unit. The organic EL display panel according to claim 1 or 2,
An organic EL display device further comprising environment estimation means for estimating an environment in which the organic EL display panel is placed according to a comparison result of the comparison means.

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